feat(p2p)!: Extend Head interface's Head method with ...HeadOption, introduce WithTrustedHead opt

headertest/dummy_header.go

@@ -115,11 +115,11 @@ func (d *DummyHeader) Verify(header header.Header) error {
 	}
 
 	if header.Height() <= d.Height() {
-		return fmt.Errorf("expected new header Height to be larger than old header Time")
+		return fmt.Errorf("expected new header Height %d to be larger than old header Height %d", header.Height(), d.Height())
 	}
 
 	if header.Time().Before(d.Time()) {
-		return fmt.Errorf("expected new header Time to be after old header Time")
+		return fmt.Errorf("expected new header Time %v to be after old header Time %v", header.Time(), d.Time())
 	}
 
 	return nil

headertest/dummy_suite.go

@@ -42,6 +42,7 @@ func (s *DummySuite) NextHeader() *DummyHeader {
 	}
 
 	dh := RandDummyHeader(s.t)
+	dh.Raw.Time = s.head.Time().Add(time.Nanosecond)
 	dh.Raw.Height = s.head.Height() + 1
 	dh.Raw.PreviousHash = s.head.Hash()
 	_ = dh.rehash()

headertest/store.go

@@ -48,7 +48,7 @@ func (m *Store[H]) Height() uint64 {
 	return uint64(m.HeadHeight)
 }
 
-func (m *Store[H]) Head(context.Context) (H, error) {
+func (m *Store[H]) Head(context.Context, ...header.HeadOption) (H, error) {
 	return m.Headers[m.HeadHeight], nil
 }
 

interface.go

@@ -127,5 +127,5 @@ type Getter[H Header] interface {
 // reporting it.
 type Head[H Header] interface {
 	// Head returns the latest known header.
-	Head(context.Context) (H, error)
+	Head(context.Context, ...HeadOption) (H, error)
 }

local/exchange.go

@@ -26,7 +26,7 @@ func (l *Exchange[H]) Stop(context.Context) error {
 	return nil
 }
 
-func (l *Exchange[H]) Head(ctx context.Context) (H, error) {
+func (l *Exchange[H]) Head(ctx context.Context, _ ...header.HeadOption) (H, error) {
 	return l.store.Head(ctx)
 }
 

opts.go

@@ -0,0 +1,17 @@
+package header
+
+type HeadOption func(opts *HeadParams)
+
+// HeadParams contains options to be used for Head interface methods
+type HeadParams struct {
+	// TrustedHead allows the caller of Head to specify a trusted header
+	// against which the underlying implementation of Head can verify against.
+	TrustedHead Header
+}
+
+// WithTrustedHead sets the TrustedHead parameter to the given header.
+func WithTrustedHead(verified Header) func(opts *HeadParams) {
+	return func(opts *HeadParams) {
+		opts.TrustedHead = verified
+	}
+}

p2p/exchange.go

@@ -3,7 +3,6 @@ package p2p
 import (
 	"bytes"
 	"context"
-	"errors"
 	"fmt"
 	"math/rand"
 	"sort"
@@ -21,10 +20,15 @@ import (
 
 var log = logging.Logger("header/p2p")
 
-// the minimum number of headers of the same height received from trusted peers
-// to determine the network head. If all trusted header will return headers with
-// non-equal height, then the highest header will be chosen.
-const minTrustedHeadResponses = 2
+// minHeadResponses is the minimum number of headers of the same height
+// received from peers to determine the network head. If all trusted peers
+// will return headers with non-equal height, then the highest header will be
+// chosen.
+const minHeadResponses = 2
+
+// numUntrustedHeadRequests is the number of head requests to be made to
+// the network in order to determine the network head.
+var numUntrustedHeadRequests = 4
 
 // Exchange enables sending outbound HeaderRequests to the network as well as
 // handling inbound HeaderRequests from the network.
@@ -72,23 +76,19 @@ func NewExchange[H header.Header](
 	return ex, nil
 }
 
-func (ex *Exchange[H]) Start(context.Context) error {
+func (ex *Exchange[H]) Start(ctx context.Context) error {
 	ex.ctx, ex.cancel = context.WithCancel(context.Background())
 	log.Infow("client: starting client", "protocol ID", ex.protocolID)
 
-	trustedPeers := ex.trustedPeers()
-
-	for _, p := range trustedPeers {
-		// Try to pre-connect to trusted peers.
-		// We don't really care if we succeed at this point
-		// and just need any peers in the peerTracker asap
-		go func(p peer.ID) {
-			err := ex.host.Connect(ex.ctx, peer.AddrInfo{ID: p})
-			if err != nil && !errors.Is(err, context.Canceled) && !errors.Is(err, context.DeadlineExceeded) {
-				log.Debugw("err connecting to a bootstrap peer", "err", err, "peer", p)
-			}
-		}(p)
+	// bootstrap the peerTracker with trusted peers as well as previously seen
+	// peers if provided. If previously seen peers were provided, bootstrap
+	// method will block until the given number of connections were attempted
+	// (successful or not).
+	err := ex.peerTracker.bootstrap(ctx, ex.trustedPeers(), numUntrustedHeadRequests)
+	if err != nil {
+		return err
 	}
+
 	go ex.peerTracker.gc()
 	go ex.peerTracker.track()
 	return nil
@@ -106,7 +106,7 @@ func (ex *Exchange[H]) Stop(ctx context.Context) error {
 // The Head must be verified thereafter where possible.
 // We request in parallel all the trusted peers, compare their response
 // and return the highest one.
-func (ex *Exchange[H]) Head(ctx context.Context) (H, error) {
+func (ex *Exchange[H]) Head(ctx context.Context, opts ...header.HeadOption) (H, error) {
 	log.Debug("requesting head")
 
 	reqCtx := ctx
@@ -121,30 +121,62 @@ func (ex *Exchange[H]) Head(ctx context.Context) (H, error) {
 		defer cancel()
 	}
 
+	reqParams := header.HeadParams{}
+	for _, opt := range opts {
+		opt(&reqParams)
+	}
+
 	var (
-		zero         H
-		trustedPeers = ex.trustedPeers()
-		headerRespCh = make(chan H, len(trustedPeers))
-		headerReq    = &p2p_pb.HeaderRequest{
+		peers           = ex.trustedPeers()
+		useTrackedPeers bool
+	)
+
+	trackedPeers, err := ex.peerTracker.getPeers(numUntrustedHeadRequests)
+	useTrackedPeers = reqParams.TrustedHead != nil && err == nil
+	// the TrustedHead field indicates whether the Exchange should use
+	// trusted peers for its Head request. If nil, trusted peers will
+	// be used. If non-nil, Exchange will ask several peers (as long as enough
+	// of them exist in the peer tracker) from its network for their Head and
+	// verify against the given trusted header.
+	if useTrackedPeers {
+		peers = trackedPeers
+	}
+
+	var (
+		zero      H
+		headerReq = &p2p_pb.HeaderRequest{
 			Data:   &p2p_pb.HeaderRequest_Origin{Origin: uint64(0)},
 			Amount: 1,
 		}
+		headerRespCh = make(chan H, len(peers))
 	)
-	for _, from := range trustedPeers {
+	for _, from := range peers {
 		go func(from peer.ID) {
 			headers, err := ex.request(reqCtx, from, headerReq)
 			if err != nil {
 				log.Errorw("head request to trusted peer failed", "trustedPeer", from, "err", err)
 				headerRespCh <- zero
 				return
 			}
+			// if tracked (untrusted) peers were requested, verify head
+			if useTrackedPeers {
+				err = reqParams.TrustedHead.Verify(headers[0])
+				if err != nil {
+					log.Errorw("head request to untrusted peer failed", "untrusted peer", from,
+						"err", err)
+					// bad head was given, block peer
+					ex.peerTracker.blockPeer(from, fmt.Errorf("returned bad head: %w", err))
+					headerRespCh <- zero
+					return
+				}
+			}
 			// request ensures that the result slice will have at least one Header
 			headerRespCh <- headers[0]
 		}(from)
 	}
 
-	headers := make([]H, 0, len(trustedPeers))
-	for range trustedPeers {
+	headers := make([]H, 0, len(peers))
+	for range peers {
 		select {
 		case h := <-headerRespCh:
 			if !h.IsZero() {
@@ -346,7 +378,7 @@ func bestHead[H header.Header](result []H) (H, error) {
 
 	// try to find Header with the maximum height that was received at least from 2 peers
 	for _, res := range result {
-		if counter[res.Hash().String()] >= minTrustedHeadResponses {
+		if counter[res.Hash().String()] >= minHeadResponses {
 			return res, nil
 		}
 	}

p2p/exchange_test.go

@@ -2,6 +2,7 @@ package p2p
 
 import (
 	"context"
+	"strconv"
 	"testing"
 	"time"
 
@@ -18,23 +19,77 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
+	"github.com/celestiaorg/go-libp2p-messenger/serde"
+
 	"github.com/celestiaorg/go-header"
 	"github.com/celestiaorg/go-header/headertest"
 	p2p_pb "github.com/celestiaorg/go-header/p2p/pb"
-	"github.com/celestiaorg/go-libp2p-messenger/serde"
 )
 
 const networkID = "private"
 
 func TestExchange_RequestHead(t *testing.T) {
-	hosts := createMocknet(t, 2)
-	exchg, store := createP2PExAndServer(t, hosts[0], hosts[1])
-	// perform header request
-	header, err := exchg.Head(context.Background())
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+
+	// decrease the minimum number of untrusted peers to request head from
+	// for testing purposes
+	numUntrustedHeadRequests = 2
+
+	hosts := createMocknet(t, 3)
+	exchg, trustedStore := createP2PExAndServer(t, hosts[0], hosts[1])
+
+	// create new server-side exchange that will act as the tracked peer
+	// it will have a higher chain head than the trusted peer so that the
+	// test can determine which peer was asked
+	trackedStore := headertest.NewStore[*headertest.DummyHeader](t, headertest.NewTestSuite(t), 50)
+	serverSideEx, err := NewExchangeServer[*headertest.DummyHeader](hosts[2], trackedStore,
+		WithNetworkID[ServerParameters](networkID),
+	)
+	require.NoError(t, err)
+	err = serverSideEx.Start(ctx)
 	require.NoError(t, err)
+	t.Cleanup(func() {
+		err = serverSideEx.Stop(ctx)
+		require.NoError(t, err)
+	})
 
-	assert.Equal(t, store.Headers[store.HeadHeight].Height(), header.Height())
-	assert.Equal(t, store.Headers[store.HeadHeight].Hash(), header.Hash())
+	tests := []struct {
+		requestFromTrusted bool
+		lastHeader         header.Header
+		expectedHeight     int64
+		expectedHash       header.Hash
+	}{
+		// routes to trusted peer only
+		{
+			requestFromTrusted: true,
+			lastHeader:         trustedStore.Headers[trustedStore.HeadHeight-1],
+			expectedHeight:     trustedStore.HeadHeight,
+			expectedHash:       trustedStore.Headers[trustedStore.HeadHeight].Hash(),
+		},
+		// routes to tracked peers and takes highest chain head
+		{
+			requestFromTrusted: false,
+			lastHeader:         trackedStore.Headers[trackedStore.HeadHeight-1],
+			expectedHeight:     trackedStore.HeadHeight,
+			expectedHash:       trackedStore.Headers[trackedStore.HeadHeight].Hash(),
+		},
+	}
+
+	for i, tt := range tests {
+		t.Run(strconv.Itoa(i), func(t *testing.T) {
+			var opts []header.HeadOption
+			if !tt.requestFromTrusted {
+				opts = append(opts, header.WithTrustedHead(tt.lastHeader))
+			}
+
+			header, err := exchg.Head(ctx, opts...)
+			require.NoError(t, err)
+
+			assert.Equal(t, tt.expectedHeight, header.Height())
+			assert.Equal(t, tt.expectedHash, header.Hash())
+		})
+	}
 }
 
 func TestExchange_RequestHead_UnresponsivePeer(t *testing.T) {
@@ -532,7 +587,7 @@ func (t *timedOutStore) HasAt(_ context.Context, _ uint64) bool {
 	return true
 }
 
-func (t *timedOutStore) Head(_ context.Context) (*headertest.DummyHeader, error) {
+func (t *timedOutStore) Head(context.Context, ...header.HeadOption) (*headertest.DummyHeader, error) {
 	time.Sleep(t.timeout)
 	return nil, header.ErrNoHead
 }